燃烧反应求解策略(2)

ISAT toleranceStart with the default 10e-3 and increase the table size from the default 100 MB To fully converge the solution decrease the ISAT tolerance and make sure that the solution is independent from any table interpolation error

EDC modelThe model is robust and stable, however in some cases tends to converge slowly, to speed up the convergence change the following option from the TUI /define/models/species> set-turb-chem-interaction Acceleration Factor [between 0 (most robust but slowest convergence) and 1] [0] The default for the edc-apmax-fac is 0, change this value with small increment (0.1), in general value above 0.5 will make the solution unstable

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Advanced FLUENT Training Combustion June 2009

Solution strategies for Deflagrations&detonations PremixedFuel and oxidizer mixed molecularly, then burn Moving reaction front – usually thin and difficult to model DeflagrationsSubsonic: very difficult to model since the flame speed depends on the chemi

stry as well as the molecular diffusion parameters, and the flame zone must be resolved.

DetonationsSupersonic: ignition due to heat release behind shock. Simpler to model than deflagrations since the shock is not resolved, and detailed molecular transport is not essential.

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ConvergenceResiduals should be less than 10-3 except for T and P-1 and species, which should be less than 10-6 The mass and energy flux reports must balanceThe fluxes can be checked from the report fluxes menu The flux report will include only heat and mass flux at the boundary (not any additional source term in the fluid or solid domain)

Monitor variables of interest (e.g. mean temperature at the outlet): solution is stable and not changing if running the case further Ensure contour plots of field variables are smooth, realistic and steady

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Species Reportsreport/species-mass-flowPrint list of species mass flow rate at inlets and outlets Available after performing 1 iteration

These options are more accurate than surface integrals at boundary zones since no interpolation is used. Report → Fluxes…

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Advanced FLUENT Training Combustion June 2009

Mass and Energy Flux Imbalance in DPM ProblemsIn DPM problems, the Report → Fluxes panel will usually give a nonzero mass and energy balance.Occurs in cases involving combustion or heat transfer from the particles/droplets to the gas phase.

In these cases the user should visit the Volume Integrals panel.Request a sum of values for DPM Mass source and DPM Enthalpy source.

At convergence, the Sum of DPM Mass Source and DPM Enthalpy Source should be equal to the Mass and Total Heat Transfer Rate imbalances in the Report Fluxes panel. For large combustion problems, this energy balance can take longer to achieve and is a better indication of convergence than low residuals.

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Customizing the reaction rateEddy dissipation/finite rate modelDEFINE_VR_RATE ( name, c, t, r, mw, yi, rr, rr_t)

Surface chemistry modelDEFINE_SR_RATE ( name, f, t, r, my, yi, rr)

Multiple char reaction modelDEFINE_PR_RATE ( name, c, t, r, mw, ci, p, sf, dif_index, cat_index, rr)

Premix model – UDF for the turbulent flame speedDEFINE_TURB_PREMIX_SOURCE ( name, c, t, turb_flame_speed, source)

Detailed chemistry modelDEFINE_NET_REACTION_RATE( name, p, temp, yi, rr, jac)

NOx modelDEFINE_NOX_RATE ( name, c, t, NOx)

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Advanced FLUENT Training Combustion June 2009

SummaryWe have tremendous in-house expertise in combustion modeling.Industrial ex

perience World-class developers and consultants

The range of physical models for combustion applications continues to grow. We are dedicated to providing better service to our customers; we appreciate and encourage your feedback! Several tutorial are available on the Learning CFD center /login/index.htmAdvanced Reacting Flow tutorial Intermediate tutorial - applications tutorials with a focus on reacting flows

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